Pathways to Realistic Impact Modelling in Estuarine Areas

Abstract

Accurately representing estuarine processes within national-scale climate and hazard models remains a major challenge for coastal flood risk and climate impact assessment. Many operational models operate at kilometre-scale resolution, which does not adequately resolve narrow estuarine channels, intertidal zones, or wetting and drying processes. As a result, key mechanisms controlling storm-surge propagation, river inflows, and salinity dynamics may be misrepresented.

This thesis evaluates how model resolution, freshwater forcing, and process parameterisation influence simulations of eight estuaries in the eastern Irish Sea during the extreme 2013–2014 storm season. High-resolution hydrodynamic simulations (grid spacing <20 m) were compared with a national-scale coupled model (~1.5 km) under like-for-like atmospheric forcing and improved river discharge conditions. In addition, simplified estuarine box models were implemented to assess whether reduced-complexity approaches can reproduce salinity dynamics and residence times under present and future climate scenarios.

Results show that increasing spatial resolution fundamentally alters simulated estuarine water levels and salinity structure. Within several kilometres of the coast, high-resolution simulations produce water levels up to 2 m higher than the national-scale model, with individual storm-surge amplification exceeding 1 m in some estuaries. Differences are strongly linked to the representation of estuarine geometry and freshwater inputs. Overestimated river discharge in the national-scale model weakens salinity gradients and modifies surge propagation inland. Box-model experiments indicate that sea-level rise is likely to increase tidal prism and accelerate flushing, reducing residence times, although impacts on stratification depend sensitively on freshwater forcing.

Overall, this work demonstrates that accurate bathymetry, realistic river climatologies, and improved estuarine parametrisations are essential for reliable national-scale hazard prediction. Incorporating these processes substantially improves projections of flooding, salinity dynamics, and climate-change impacts in UK estuaries.

Date of Award	27 Mar 2026
Original language	English
Awarding Institution	Bangor University
Sponsors	Met Office
Supervisor	Peter Robins (Supervisor), Simon Neill (Supervisor) & Huw Lewis (Supervisor)